torsdag den 31. juli 2008

We knew the web was big...

Google er stor eller rettere nettet er stort - rigtig stort. Og igen, nettet er blot en reflektion af hvad vi er, som mennesker, som individer, som grupper osv. Med nettet og med Google (og andre) har vi for første gang i historien adgang til data, til informationer og meget meget mere. Det giver os alle et nyt fundament at agere på og træffe beslutninger ud fra - blive klog på og atter igen skabe ny viden og ny information. Google er stor, men kan kun blive større med tiden.

Google is gigantic or rather the Internet is gigantic - Gigantic with a capital G. And then again however, it is merely a reflection of what we are as humans, as individuals, as groups etc. With the Internet and Google (and others alike) we have for the first time in history access to large resources of data and information and a lot more. This gives us a solid foundation on which to act and draw important decisions - we get more informed and on this basis creates new knowledge and new information. Google is big, but it will never cease to grow.


We knew the web was big...

We've known it for a long time: the web is big. The first Google index in 1998 already had 26 million pages, and by 2000 the Google index reached the one billion mark. Over the last eight years, we've seen a lot of big numbers about how much content is really out there. Recently, even our search engineers stopped in awe about just how big the web is these days -- when our systems that process links on the web to find new content hit a milestone: 1 trillion (as in 1,000,000,000,000) unique URLs on the web at once!

How do we find all those pages? We start at a set of well-connected initial pages and follow each of their links to new pages. Then we follow the links on those new pages to even more pages and so on, until we have a huge list of links. In fact, we found even more than 1 trillion individual links, but not all of them lead to unique web pages. Many pages have multiple URLs with exactly the same content or URLs that are auto-generated copies of each other. Even after removing those exact duplicates, we saw a trillion unique URLs, and the number of individual web pages out there is growing by several billion pages per day.

So how many unique pages does the web really contain? We don't know; we don't have time to look at them all! :-) Strictly speaking, the number of pages out there is infinite -- for example, web calendars may have a "next day" link, and we could follow that link forever, each time finding a "new" page. We're not doing that, obviously, since there would be little benefit to you. But this example shows that the size of the web really depends on your definition of what's a useful page, and there is no exact answer.

We don't index every one of those trillion pages -- many of them are similar to each other, or represent auto-generated content similar to the calendar example that isn't very useful to searchers. But we're proud to have the most comprehensive index of any search engine, and our goal always has been to index all the world's data.

To keep up with this volume of information, our systems have come a long way since the first set of web data Google processed to answer queries. Back then, we did everything in batches: one workstation could compute the PageRank graph on 26 million pages in a couple of hours, and that set of pages would be used as Google's index for a fixed period of time. Today, Google downloads the web continuously, collecting updated page information and re-processing the entire web-link graph several times per day. This graph of one trillion URLs is similar to a map made up of one trillion intersections. So multiple times every day, we do the computational equivalent of fully exploring every intersection of every road in the United States. Except it'd be a map about 50,000 times as big as the U.S., with 50,000 times as many roads and intersections.

As you can see, our distributed infrastructure allows applications to efficiently traverse a link graph with many trillions of connections, or quickly sort petabytes of data, just to prepare to answer the most important question: your next Google search.

Posted by Jesse Alpert & Nissan Hajaj, Software Engineers, Web Search Infrastructure Team


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